So far, generation of broadly neutralizing antibody responses against diverse primary HIV isolates has been[unreadable] an elusive target. Therefore, the aim of this project is to design and evaluate novel Env immunogens for their[unreadable] ability to induce broadly neutralizing antibody responses against diverse primary isolates. We previously[unreadable] reported that an Env immunogen (o-gp140SF162DV2) containing a partial deletion in the second variable[unreadable] loop (V2) derived from SF162 (R5 tropic), when used in a DMA prime-protein boost regimen in rhesus[unreadable] macaques, induced neutralizing antibodies against some heterologous subtype B primary isolates as well as[unreadable] protection to the vaccinated animals upon challenge with pathogenic SHIVSF162P4. We plan to continue[unreadable] working on trimeric Env and use four complementary approaches to further enhance the exposure of[unreadable] conserved neutralizing epitopes to improve the efficacy of Env immunogens in inducing broadly neutralizing[unreadable] antibodies and protection in challenge model. In the first, we propose to increase the exposure of conserved[unreadable] neutralizing epitopes involved in receptor and co-receptor binding regions of the Env by introducing deletions[unreadable] in V-regions and "bridging-sheet" following rational and random approaches. In the second, we seek to[unreadable] expose neutralizing epitopes by introducing site specific or global deglycosylation either alone or in[unreadable] combination with b-sheet and/or V- loops. In the third, we seek to expose these epitopes by the use of Env[unreadable] complexed to rationally designed CD4 mimics or other scaffolds. Lastly, we propose to express Env trimer in[unreadable] non-glycosylated form to enhance the exposure of critical neutralizing epitopes that are shielded by[unreadable] extensive glycosylation. We will use subtype B antigens as a model for evaluating the efficacy of various[unreadable] approaches mentioned above. The best approach will be used for optimizing Env antigens from other[unreadable] subtypes e.g. A and C. We will screen candidate immunogens for expression, CD4-binding, and binding to a[unreadable] panel of monoclonal antibodies of known specificities. Once a candidate has met pre-defined criteria, it then[unreadable] will be advanced to immunogenicity studies in rabbits. Neutralizing antibody and cellular responses induced[unreadable] by the lead candidate will be optimized using adjuvants, formulations, and vaccine regimens. The best Env[unreadable] immunogen will be advanced to vaccine/challenge studies in primates. These studies should yield important[unreadable] information for the design of next generation HIV vaccines for future clinical evaluations.[unreadable]